学习目标

学习openGuass数据库中如何对表进行修改

课程学习

1、创建表

omm=# --首先创建一张测试表。
omm=# drop table if exists test;
NOTICE:  table "test" does not exist, skipping
DROP TABLE
omm=# create table test(
      id bigint,
omm(# omm(#       name varchar(50) not null,
      age  int default 20,
omm(# omm(#       primary key(id)
omm(#      );
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "test_pkey" for table "test"
CREATE TABLE

2、为表添加字段

omm=# --查看表test的信息
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

omm=# 
omm=# omm=# --为表test新增一列，列名为sex，数据类型为Boolean：
alter table test add column sex Boolean;
ALTER TABLE
omm=# 
omm=# --执行下面gsql命令，查看表test的信息
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
 sex    | boolean               | 
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

3、删除表中的已有字段

root@modb:~# su - omm
omm@modb:~$ gsql -r
gsql ((openGauss 3.0.0 build 02c14696) compiled at 2022-04-01 18:12:00 commit 0 last mr  )
Non-SSL connection (SSL connection is recommended when requiring high-security)
Type "help" for help.

omm=# --执行下面的SQL语句，删除刚刚添加的列sex：
omm=# alter table test drop column sex ;
ALTER TABLE
omm=# 
omm=# --执行下面gsql命令，再次查看表test的信息
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 20
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

4、删除表的已有约束

omm=# --执行下面的gsql命令，再次查看表test的信息：
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not nullomm=# 
 age    | integer               | default 20

omm=# 
--或直接查看约束是否被删除
omm=# select * from pg_constraint  where conname like 'test_pkey';
 conname | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | confdeltype 
| confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conbin
 | consrc | conincluding 
---------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-------------
+---------------+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+-------
-+--------+--------------
(0 rows)

5、为表添加约束

omm=# --执行下面的SQL命令，为表test添加刚刚删除的主键约束：
omm=# alter table test add constraint test_pkey primary key(id);
NOTICE:  ALTER TABLE / ADD PRIMARY KEY will create implicit index "test_pkey" for table "test"
ALTER TABLE
omm=# 
omm=# --再次查看表test的信息：
omm=# select * from pg_constraint  where conname like 'test_pkey';
  conname  | connamespace | contype | condeferrable | condeferred | convalidated | conrelid | contypid | conindid | confrelid | confupdtype | confdeltyp
e | confmatchtype | conislocal | coninhcount | connoinherit | consoft | conopt | conkey | confkey | conpfeqop | conppeqop | conffeqop | conexclop | conb
in | consrc | conincluding 
-----------+--------------+---------+---------------+-------------+--------------+----------+----------+----------+-----------+-------------+-----------
--+---------------+------------+-------------+--------------+---------+--------+--------+---------+-----------+-----------+-----------+-----------+-----
---+--------+--------------
 test_pkey |         2200 | p       | f             | f           | t            |    16389 |        0 |    16395 |         0 |             |           
  |               | t          |           0 | t            | f       | f      | {1}    |         |           |           |           |           |     
   |        | 
(1 row)

6、修改表字段的默认值

omm=# --执行下面的SQL语句，将age的默认值变更为25
omm=# alter table test alter column age set default 25;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | integer               | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

7、修改表字段的数据类型

omm=# alter table test ALTER COLUMN age TYPE bigint;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 age    | bigint                | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

8、修改表字段的名字

omm=# ALTER TABLE test RENAME COLUMN age TO stuage;
ALTER TABLE
omm=# \d test
             Table "public.test"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

9、修改表的名字

omm=# --修改表的名字。执行下面的SQL语句，将表test的名字变更为mytest：
omm=# ALTER TABLE test RENAME TO mytest;
ALTER TABLE
omm=# \d mytest
            Table "public.mytest"
 Column |         Type          | Modifiers  
--------+-----------------------+------------
 id     | bigint                | not null
 name   | character varying(50) | not null
 stuage | bigint                | default 25
Indexes:
    "test_pkey" PRIMARY KEY, btree (id) TABLESPACE pg_default

10、删除表

omm=# DROP TABLE mytest;
DROP TABLE
omm=# 

学习总结

今天继续学习对表的操作，包含为表加字段，删字段，加约束，删约束，修改表字段名字，修改表字段类型，修改表的名字，删除表，命令还是容易理解的，跟mysql的命令没啥差别，比较简单适合入门。